1. Field of the Invention
This invention relates to systems and methods for maximizing the dissolution concentration of a single gas species in a liquid from a source gas containing multiple species of gases. More specifically, this invention is directed to systems and methods for maximizing the concentration of dissolved ozone gas in a liquid, such as water, by periodically or continuously dissolving ozone in the liquid that is sprayed through a gas feed of ozone and oxygen while removing excess oxygen gas from the headspace of the saturation tank used in the dissolution system.
2. Background of the Related Art
Many different systems and methods are available for dissolving gases in liquids and are highly dependent on the needed application. Some of the main applications that require dissolving gases into liquids include the oxygenation of outdoor water bodies, industrial uses, and the treatment of wastewater and drinking water. Most dissolved gas delivery methods—bubble diffusion, Venturi injection, U-tubes, and Speece cones, for example—are based on increasing the contact time or surface area of gas bubbles introduced into a bulk liquid to enhance mass transfer. Previous technologies for dissolving gas into a liquid have features that increase the contact time or contact area between gas bubbles and the bulk fluid to increase dissolution.
Most, if not all, of these earlier technologies require recovery systems for off-gases that do not dissolve into the fluid or allow loss of undissolved gases. For example, U.S. Pat. No. 5,979,363 to Shaar describes an aquaculture system that involves piping a food and oxygen slurry into a pond. U.S. Pat. No. 5,911,870 to Hough discloses a device for increasing the quantity of dissolved oxygen in water and employs an electrolytic cell to generate the oxygen. U.S. Pat. No. 5,904,851 to Taylor discloses a method for enriching water with oxygen that employs a Venturi-type injector to aspirate gas into a fluid, followed by mixing to increase dissolution. U.S. Pat. No. 5,885,467 to Zelenak discloses mixing a liquid with oxygen using a plurality of plates or trays over which the liquid flows gradually downward. U.S. Pat. No. 4,501,664 to Heil discloses a device for treating organic wastewater with dissolved oxygen that employs several process compartments. U.S. Pat. No. 5,766,484 to Petit describes a dissolved gas flotation system for treatment of wastewater wherein the relative location of inlet and outlet structures reportedly maximizes the effect of air bubbles in separating solids from the fluid. U.S. Pat. No. 5,647,977 to Arnaud describes a system for treating wastewater that includes aeration, mixing/flocculating, and contact media for removing suspended solids. U.S. Pat. No. 5,382,358 to Yeh discloses an apparatus for separation of suspended matter in a liquid by dissolved air flotation. And U.S. Pat. No. 3,932,282 to Ettelt discloses a dissolved air flotation system that includes a vertical flotation column designed with an aim of preventing bubble breakage.
Other U.S. patents describe various methods of increasing the contact time between gas bubbles in fluids, including U.S. Pat. No. 5,275,742 to Satchell; U.S. Pat. No. 5,451,349 to Kingsley; U.S. Pat. No. 5,865,995 to Nelson; U.S. Pat. No. 6,076,808 to Porter; U.S. Pat. No. 6,090,294 to Teran; U.S. Pat. No. 6,503,403 to Green; and U.S. Pat. No. 6,840,983 to McNulty. Spears, et al. (U.S. Pat. Nos. 7,294,278; 7,008,535) describe a method for varying the dissolved oxygen concentration in a liquid by varying the pressure from 14.7 to 3000 psi inside an oxygenation assembly. Patterson, et al. (U.S. Pat. No. 6,565,807) describe a method for maintaining, adjusting, or otherwise controlling the levels of oxygen dissolved in blood (e.g., pO2) by controlling the flow rates or by providing controlled amounts of the blood or oxygen gas.
These conventional systems for dissolving gases in liquids, and in particular conventional dissolved ozone delivery systems, are based on dissolving bubbles into stationary or flowing water and are greatly limited in the range of dissolved ozone concentration that can be attained and controlled. These conventional systems are also limited to nearly continuous use at constant dissolved ozone concentration, and cannot quickly adjust dissolved ozone concentrations to optimize water treatment cost and effectiveness. Bubble-based technology is limited to much lower dissolved ozone concentration in the water being treated because of lower pressure and less-efficient gas transfer.
U.S. Pat. No. 7,255,332, issued to the present inventor and incorporated herein by reference in its entirety, discloses a system and method for dissolving gases in fluids and for the delivery of dissolved gases. The system disclosed in U.S. Pat. No. 7,255,332 includes a saturation tank, a high pressure liquid pump in fluid communication with the tank, and a pressurized gas source in communication with a regulated gas headspace of the saturation tank. The saturation tank includes a pressure vessel for containing the liquid and has a pressure regulated gas headspace above the liquid, which contains at least one inlet that permits passage of liquid into the pressure vessel, and an outlet for the liquid containing dissolved gas. Upon passing the gas-containing liquid into a second fluid, the gas dissolved in the liquid is released to the water being treated in dissolved form. U.S. application Ser. No. 13/415,402, filed on Mar. 8, 2012, and entitled SYSTEM AND METHOD FOR OPTIMIZING THE DISSOLUTION OF A GAS IN A LIQUID, describes an improvement to the system disclosed in U.S. Pat. No. 7,255,332. FIG. 1 illustrates the system described in U.S. application Ser. No. 13/415,402 which optimizes and controls the dissolution of ozone or other gas in a liquid within a pressure vessel by regulating vessel pressure, flow rate of a liquid into the vessel, retention time of the gas and liquid in the vessel, gas flow rate, liquid spray pattern, and internal mixing within the vessel. The optimal operating vessel pressure, flow rate of the liquid, retention time of the gas and liquid in the vessel, gas flow rate, liquid spray pattern, and internal mixing within the vessel may be determined based on the operating characteristics of an ozone generator.
In comparison to the systems described previously in this disclosure, the systems disclosed in U.S. Pat. No. 7,255,332 and U.S. application Ser. No. 13/415,402 are capable of providing superior dissolved gas levels in a liquid. However, in ozone applications the rate of dissolved ozone delivered from the system will be at a maximum when the unit is first activated, but will fall to a lower steady-state rate within 15 minutes.
Accordingly, there is a need for systems and methods for continuing to maximize the concentration of a gas dissolved in a liquid. The systems and methods described in this disclosure meet this need.